scholarly journals The role of crystal fabric in flow near an ice divide

2007 ◽  
Vol 53 (181) ◽  
pp. 277-288 ◽  
Author(s):  
Erin C. Pettit ◽  
Throstur Thorsteinsson ◽  
H. Paul Jacobson ◽  
Edwin D. Waddington
Keyword(s):  
Flow Pattern ◽  
Large Scale ◽  
Cone Angle ◽  
West Antarctica ◽  
Crystal Preferred Orientation ◽  
Siple Dome ◽  
Polycrystalline Ice ◽  
Measured Profile ◽  
Large Scale Flow

AbstractPolycrystalline ice near an ice divide typically shows a crystal fabric (crystal preferred orientation) with c axes clustered vertically. We explore the effect of this fabric on the large-scale flow pattern near an ice divide. We incorporate an analytical formulation for anisotropy into a non-linear flow law within a finite-element ice-sheet flow model. With four different depth profiles of crystal fabric, we find that the effect of fabric is significant only when a profile has a minimum cone angle of less than ~25º. For a steady-state divide, the shape and size of the isochrone arch can depend as much on the crystal fabric as it does on the non-linearity of ice flow. A vertically oriented fabric tends to increase the size of the isochrone arch, never to reduce it. Also, non-random fabric has little effect on the ice-divide-flow pattern when ice is modeled as a linear (Newtonian) fluid. Finally, when we use a crystal-fabric profile that closely approximates the measured profile for Siple Dome, West Antarctica, the model predicts concentrated bed-parallel shearing 300 m above the bed.

Intraseasonal to decadal variability of Rossby wave packet properties

2021 ◽  
Author(s):  
Georgios Fragkoulidis ◽  
Volkmar Wirth
Keyword(s):  
Rossby Wave ◽  
Large Scale ◽  
Decadal Variability ◽  
Phase Speed ◽  
Diagnostic Methods ◽  
Temperature And Precipitation ◽  
Ongoing Work ◽  
Large Scale Flow

<p>The large-scale extratropical upper-tropospheric flow tends to organize itself into eastward-propagating Rossby wave packets (RWPs). Investigating the spatiotemporal evolution of RWPs and the underlying physical processes has been beneficial in showcasing the role of the upper-tropospheric flow in temperature and precipitation extremes. The use of recently developed diagnostics of local in space and time wave properties has provided further insight in this regard. Motivated by the above, these diagnostic methods are now being employed to investigate the intraseasonal to decadal variability of key RWP properties such as their amplitude, phase speed, and group velocity in reanalysis datasets. It is shown that these properties exhibit a distinct seasonal and interregional variability, while interesting patterns thereof emerge. Moreover, the interannual and long-term variability in these RWP properties is explored and significant decadal trends for specific regions and seasons are highlighted. Ongoing work aims at further utilizing the presented diagnostics and analyses toward an improved understanding of the extratropical large-scale flow variability from weather to climate time scales.</p>

scholarly journals Excitation of twin-vortex flow in the nightside high-latitude ionosphere during an isolated substorm

2002 ◽  
Vol 20 (10) ◽  
pp. 1577-1601 ◽  
Author(s):  
A. Grocott ◽  
S. W. H. Cowley ◽  
J. B. Sigwarth ◽  
J. F. Watermann ◽  
T. K. Yeoman
Keyword(s):  
Flow Pattern ◽  
High Latitude ◽  
Large Scale ◽  
Local Times ◽  
Closed Field ◽  
Plasma Convection ◽  
Expansion Phase ◽  
Ionospheric Conductivity ◽  
Large Scale Flow ◽  
Open Flux

Abstract. We present SuperDARN radar observations of the ionospheric flow during a well-observed high-latitude substorm which occurred during steady northward IMF conditions on 2 December 1999. These data clearly demonstrate the excitation of large-scale flow associated with the substorm expansion phase, with enhanced equatorward flows being observed in the pre-midnight local time sector of the expansion phase auroral bulge and westward electrojet, and enhanced return sunward flows being present at local times on either side, extending into the dayside sector. The flow pattern excited was thus of twin-vortex form, with foci located at either end of the substorm auroral bulge, as imaged by the Polar VIS UV imager. Estimated total transpolar voltages were ~40 kV prior to expansion phase onset, grew to ~80 kV over a ~15 min interval during the expansion phase, and then decayed to ~35 kV over ~10 min during recovery. The excitation of the large-scale flow pattern resulted in the development of magnetic disturbances which extended well outside of the region directly disturbed by the substorm, depending upon the change in the flow and the local ionospheric conductivity. It is estimated that the nightside reconnection rate averaged over the 24-min interval of the substorm was ~65– 75 kV, compared with continuing dayside reconnection rates of ~30–45 kV. The net closure of open flux during the sub-storm was thus ~0.4–0.6 × 108 Wb, representing ~15–20% of the open flux present at onset, and corresponding to an overall contraction of the open-closed field line boundary by ~1° latitude.Key words. Ionosphere (auroral ionosphere; ionosphere-magnetosphere interactions; plasma convection)

scholarly journals A simulation study demonstrating the importance of large-scale trailing vortices in wake steering

2018 ◽  
Vol 3 (1) ◽  
pp. 243-255 ◽  
Author(s):  
Paul Fleming ◽  
Jennifer Annoni ◽  
Matthew Churchfield ◽  
Luis A. Martinez-Tossas ◽  
Kenny Gruchalla ◽  
...  
Keyword(s):  
Power Generation ◽  
Simulation Study ◽  
Large Scale ◽  
Wind Farm ◽  
Flow Structures ◽  
New Model ◽  
Trailing Vortices ◽  
Engineering Models ◽  
Large Scale Flow

Abstract. In this paper, we investigate the role of flow structures generated in wind farm control through yaw misalignment. A pair of counter-rotating vortices is shown to be important in deforming the shape of the wake and in explaining the asymmetry of wake steering in oppositely signed yaw angles. We also demonstrate that vortices generated by an upstream turbine that is performing wake steering can deflect wakes of downstream turbines, even if they are themselves aligned. We encourage the development of improvements to control-oriented engineering models of wind farm control, to include the effects of these large-scale flow structures. Such a new model would improve the predictability of control-oriented models. Further, we demonstrate that the vortex structures created in wake steering can lead to greater impact on power generation than currently modeled in control-oriented models. We propose that wind farm controllers can be made more effective if designed to take advantage of these effects.

scholarly journals The Key Role of Diabatic Outflow in Amplifying the Midlatitude Flow: A Representative Case Study of Weather Systems Surrounding Western North Pacific Extratropical Transition

2016 ◽  
Vol 144 (10) ◽  
pp. 3847-3869 ◽  
Author(s):  
Christian M. Grams ◽  
Heather M. Archambault
Keyword(s):  
Flow Pattern ◽  
North Pacific ◽  
Western North Pacific ◽  
Large Scale ◽  
Wave Pattern ◽  
Conveyor Belt ◽  
Rain Event ◽  
Extratropical Transition ◽  
The North

Recurving tropical cyclones (TCs) undergoing extratropical transition (ET) may substantially modify the large-scale midlatitude flow pattern. This study highlights the role of diabatic outflow in midlatitude flow amplification within the context of a review of the physical and dynamical processes involved in ET. Composite fields of 12 western North Pacific ET cases are used as initial and boundary conditions for high-resolution numerical simulations of the North Pacific–North American sector with and without the TC present. It is demonstrated that a three-stage sequence of diabatic outflow associated with different weather systems is involved in triggering a highly amplified midlatitude flow pattern: 1) preconditioning by a predecessor rain event (PRE), 2) TC–extratropical flow interaction, and 3) downstream flow amplification by a downstream warm conveyor belt (WCB). An ensemble of perturbed simulations demonstrates the robustness of these stages. Beyond earlier studies investigating PREs, recurving TCs, and WCBs individually, here the fact that each impacts the midlatitude flow through a similar sequence of processes surrounding ET is highlighted. Latent heat release in rapidly ascending air leads to a net transport of low-PV air into the upper troposphere. Negative PV advection by the diabatically driven outflow initiates ridge building, accelerates and anchors a midlatitude jet streak, and overall amplifies the upper-level Rossby wave pattern. However, the three weather systems markedly differ in terms of the character of diabatic heating and associated outflow height, with the TC outflow reaching highest and the downstream WCB outflow producing the strongest negative PV anomaly.

scholarly journals Role of the Low-Frequency Deformation Field on the Explosive Growth of Extratropical Cyclones at the Jet Exit. Part II: Baroclinic Critical Region

2006 ◽  
Vol 63 (8) ◽  
pp. 1982-1995 ◽  
Author(s):  
G. Rivière ◽  
A. Joly
Keyword(s):  
Critical Region ◽  
High Frequency ◽  
Large Scale ◽  
Intermediate Phase ◽  
Low Frequency ◽  
Atmospheric Flow ◽  
Upper Level ◽  
Large Scale Flow ◽  
Upper Level Jet

Abstract Midlatitude cyclones tend to develop strongly in specific locations relative to the large-scale flow, such as jet-exit zones. Here, the approach developed in Part I that highlights the role of large-scale deformation in constraining the location of such events is continued. The atmospheric flow is decomposed into a high- and low-frequency part separating large and synoptic scales. A new low-frequency diagnostic has been introduced, called effective deformation Δm. It is defined as σ2m − ζ2m, where σm is the low-frequency deformation magnitude and ζm is the low-frequency vorticity. While Part I focused on large-scale conditions inducing an intermediate phase of barotropic growth, the present paper concentrates on other configurations that rather prevent this phase from happening. This large-scale circulation is characterized by the presence of a strong zonal upper-level jet and a lower-level jet that are meridionally quite far from each other over the Atlantic but close to one another in the eastern Atlantic region. As high-frequency disturbances are trapped by the effective deformation of the low-frequency jets, the increasing closeness of the two jets associated with that of the two effective deformation fields computed in the lower and upper levels defines a region called the baroclinic critical region where upper high-frequency disturbances and surface cyclones may strongly interact baroclinically. The increased baroclinic energy collection resulting from this constrained configuration change is outlined. An analysis of the explosive growth of the Christmas wind storms of 1999 and of mid-December 2004 provides different realizations of this configuration and associated mechanism.

scholarly journals Electron hydrodynamics in anisotropic materials

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
Georgios Varnavides ◽  
Adam S. Jermyn ◽  
Polina Anikeeva ◽  
Claudia Felser ◽  
Prineha Narang
Keyword(s):  
Flow Pattern ◽  
Time Reversal ◽  
Large Scale ◽  
Three Dimensional ◽  
Anisotropic Materials ◽  
Three Dimensions ◽  
Time Reversal Symmetry ◽  
Classical Fluids ◽  
Large Scale Flow ◽  
Breaking Time

Abstract Rotational invariance strongly constrains the viscosity tensor of classical fluids. When this symmetry is broken in anisotropic materials a wide array of novel phenomena become possible. We explore electron fluid behaviors arising from the most general viscosity tensors in two and three dimensions, constrained only thermodynamics and crystal symmetries. We find nontrivial behaviors in both two- and three-dimensional materials, including imprints of the crystal symmetry on the large-scale flow pattern. Breaking time-reversal symmetry introduces a non-dissipative Hall component to the viscosity tensor, and while this vanishes for 3D isotropic systems we show it need not for anisotropic materials. Further, for such systems we find that the electronic fluid stress can couple to the vorticity without breaking time-reversal symmetry. Our work demonstrates the anomalous landscape for electron hydrodynamics in systems beyond graphene, and presents experimental geometries to quantify the effects of electronic viscosity.

The Role of Sense of Direction and Other Factors During Navigation in a Large-Scale, Unconstrained Environment

2013 ◽  
Author(s):  
Elisabeth J. Ploran ◽  
Ericka Rovira ◽  
James C. Thompson ◽  
Raja Parasuraman
Keyword(s):  
Large Scale ◽  
Sense Of Direction
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